Z₂Vortex-Induced Broadening of the EPR Linewidth in the Two-Dimensional Triangular Lattice Antiferromagnets, HCrO₂and LiCrO₂

The title compounds are the family of the AMO ₂ -type (R\bar3m) crystal which has a pronounced layer structure and are promising candidates for the two-dimensional Heisenberg triangular lattice antiferromagnet (2DH TAL-AF). The interesting observation is that a singular point of the EPR signal is located around T _KM =0.66 J S ² for the critical temperature of phase transition associated with the pairing-dissociation of the Z ₂ vortices, suggesting the present system behaves as 2DH TAL-AF down to very close to T _KM . The EPR linewidth exhibits Z ₂ vortex-induced broadening above the critical temperature which is inversely proportional to the thermally excited vortex density, n _v ∝exp (- E _v / k _B T ) with the activation energy \(E_{\text{v}}{\cong}4k_{\text{B}}T_{\text{KM}}\).